Hot melt adhesives are known, for instance, in the JP 2001787 describing tacky adhesive compositions for tapes comprising a block copolymer of a vinylaromatic hydrocarbon and a high vinyl polybutadiene block. The composition comprises a block copolymer, a tackifying resin and at least one phenol compound. The block copolymer is composed of at least one polymeric block mainly containing butadiene. It has a vinylaromatic hydrocarbon content of 10-36% by weight and the butadiene portions have a vinyl content of 15-55%.
The JP 63182386 discloses tacky block copolymer compositions containing a vinylaromatic-butadiene block copolymer, a tackifying resin and a phenolic compound. The block copolymer is mainly composed of vinylaromatic hydrocarbon and at least one polymer block composed of polybutadiene.
The EP-A-0 243 956 discloses an adhesive composition comprising a block copolymer containing at least one vinylaromatic hydrocarbon block and one butadiene containing block, wherein the relationship between the vinylaromatic hydrocarbon block and the 1,2-vinyl content in the butadiene portion is within a ratio between 40 and 70. In addition, the polymers that have been used have a melt flow rate of 5 g/10 min. (200° C., 5 kg).
These hot melt compositions however do not have the same properties as those based on SIS in respect of tack, adhesive strength creep resistance and treatment capacity at high temperature.
The object of the invention is a hot melt adhesive composition having equal or better properties compared to prior art adhesives, especially poly(styrene-isoprene-styrene) (SIS) based adhesives.
Poly(styrene-butadiene-styrene) polymers are currently used in pressure sensitive adhesives despite their high viscosity, poor thermal stability, and poor processability. The main reason for this is their high viscosity and tendency to cross-link so that the processing step becomes a limiting factor. Surprisingly a block copolymer composition including a diblock copolymer (i) having one block of a monovinylaromatic hydrocarbon and one block of a conjugated diene and one or more block copolymers (ii) comprising at least two blocks of monovinylaromatic hydrocarbon and at least one block of conjugated diene has been developed with molecular parameters suitable for hot melt adhesive applications.